Solitary plasmacytoma of bone (SPB) occurs infrequently, therefore no clear prognostic factors for this ailment, when treated with radiotherapy alone, have been established. Evolving criteria regarding the definition of SPB and limited information regarding pre and post-treatment serum and urine protein levels have also made this difficult.

The purpose of this study was to determine what prognostic factors, if any, exist.

Materials and Methods

63 patients were identified at the M.D. Anderson Cancer Center treated for SPB between 1963 and 2000. The diagnosis of SPB was determined by: < 5% plasma cells in bone marrow, only one identifiable bony lesion, normal serum calcium and creatinine and serum M protein < 3.0g/dL. 60 of these patients were treated with radiotherapy alone. Only these patients were analyzed.

Median size of the plasmacytoma was 3 cm. 40% of lesions were vertebral, 15% were pelvic bone and 13% were in the rib.

On multivariate analysis, the only independent prognostic factor for MFS and CSS was found to be persistence of M protein for more than one year following radiation treatment. 10 year MFS in those with no M protein at one year was 91% vs. 29% in those with persistent M protein (p=0.005). Most of those with persistence of M protein subsequently developed multiple myeloma.

All patients with a serum M protein > 1.0 g/dL at diagnosis had persistence of M protein post treatment.

46 of 60 patients had an associated soft tissue mass. This was not shown to be prognostically significant.

Author's Conclusions

Patients with persistent M protein after radiation treatment for SPB should be carefully followed and should be considered for standard multiple myeloma induction chemotherapy followed by intensive consolidation when they become symptomatic.

MRI of the thoracic and lumbar spine should be strongly considered in all case of SPB to rule out multiple bony lesions and the subsequent diagnosis of multiple myeloma.

Clinical/Scientific Implications In this retrospective analysis of a relatively small number of patients, only the persistence of M protein more than one year following radiation therapy was an independent prognostic factor for MFS and CSS. This study has helped to identify a high-risk subset of SPB patients that may be a increased risk for progression to multiple myeloma and who may benefit from multiple myeloma chemotherapy. Further research with larger patient populations would be helpful in identifying other prognostic factors that surely exist but have yet to be discovered.

Oncolink's ASH Coverage made possible by an unrestricted Educational Grant from Amgen.